saving an icon to shared preference in flutter

I am still struggling to save an iconData to the devices storage for my to-do app, I get this error:

Converting object to an encodable object failed: Instance of 'IconData'

in the debug console while adding the to-do item.

If I take out the iconData, the To-Do item is saving correctly, and when I put it back in, I get that error.

import 'package:flutter/foundation.dart';

class ToDo{
  final String id;
  final String title;

  final IconData icon;

  const ToDo({
    @required this.id, 
    @required this.title,
    @required this.icon,

  });

  Category.fromMap(
    Map map,
  )   :

        this.id = map['id'],
        this.title = map['title'],
        this.icon = map['icon'],

  Map toMap() {
    return {  
      'id': this.id,
      'title': this.title,
      'icon': this.icon,

    };
  }

}

and in my main script I have

  List<ToDo> _userToDo = List<ToDO>();

  SharedPreferences sharedPreferences;
  @override
  void initState() {
    initSharedPreferences();
    super.initState();
  }

  initSharedPreferences() async {
    sharedPreferences = await SharedPreferences.getInstance();
    loadDataTodo();

  }

  void saveDataTodo() {
    List<String> spList = _userTodo
        .map((todo) => json.encode(todo.toMap()))
        .toList();
    sharedPreferences.setStringList(todo, spList);
  }

  void loadDataTodo() {
    List<String> spList = sharedPreferences.getStringList(todo);
    _userTodo = spList
        .map((todo) => todo.fromMap(json.decode(todo)))
        .toList();
    setState(() {});
  }

Please help me - I am new to flutter

Solution 1: krumpli

setState in loadDataTodo isn't doing much unless you do this:

void loadDataTodo() {
    List<String> spList = sharedPreferences.getStringList(todo);
    setState(() {
       _userTodo = spList
        .map((todo) => todo.fromMap(json.decode(todo)))
        .toList();
    });
  }

Try printing _userTodo and check if it's empty after this change.

sharedPreferences.setStringList(todo, spList) //todo should be a string.